The present invention relates to improvements in papermaking machines and more specifically to a headbox and forming zone arrangement for delivering a controlled flow of stock to a forming zone.
Developments in the papermaking field relative to delivering a jet of stock from a pressure headbox to a forming zone have included improvements such as turning bars over which the wires are trained, vanes in the headbox and bladed forming zone arrangements which tend to eliminate the need for a free jet of stock. The headbox and former become a single unit with the ability to totally control the activity of the approached flow of stock without free surface instability. Limitations to the development of sheet quality, particularly where multiple layers are required, exist in the free jet which has heretofore been controlled by a profiling bar or slice lip.
In multiple layered paper, good layer purity has been limited by the control restrictions to permit a headbox jet to pass through free air until it has been placed under control by the forming zone. Excess activity of the free jet causes the jet to break up. The need for a protruding slice bar causes discharge vortexes which generate layer mixing.